As is well known to those skilled in the art, waste water may contain a wide variety of undesirable components which may restrict its use or disposal by passage to natural bodies of water. Illustrative of industrial waters which may normally be discharged into adjoining bodies of water is the aqueous discharge from an oil production platform. These platforms are constructed in fresh water lakes or more commonly in salt water bodies in which drilling is carried out and in due course production of hydrocarbons. Prior to further treatment of the hydrocarbons it is necessary to separate them from the produced water which is passed to waste.
Produced water contains a wide variety of components depending upon the details of operation. It may contain dissolved water-soluble salts typified by those present in sea water, which commonly contains the following:
TABLE ______________________________________ Element Parts per Million (w) ______________________________________ Cl 18,980 Na 10,561 Mg 1,272 S 884 Ca 400 K 380 Br 65 C (inorg) 28 Sr 13 (SiO.sub.2) 0.01-7.0 B 4.6 Si 0.02-4.0 C (org) 1.2-3.0 Al 0.16-1.9 F 1.4 ______________________________________
Many other elements may be present in amounts each less than about 1 ppm. See Handbook of Chemistry and Physics (44 Ed) 1962, Page 3488.
Commonly sea water is considered as being a dilute solution of sodium chloride containing about 3.5 w% thereof.
In typical production platforms, as the hydrocarbon is recovered from the undersea sources, there is discharged a substantial portion of produced water including formation water and injected water. Formation water is that water which is naturally present in the oil or gas reservoir. This may amount to as little as less than 1 v% at the beginning of production but typically increases during the life of the well. Injected water is typically sea water which has been injected into the well to enhance the recovery of hydrocarbon (See for example Somerville et al Environmental Effect of Produced water from North Sea Oil Operations Marine Pollution Bulletin Vol 18, No 10, pp 549-558 (1987) Great Britain).
Produced water may contain non-hydrocarbon organic matter, largely as salts of lower aliphatic carboxylic acids such as acetic, propionic, butyric acids, commonly in amounts up to about one gram per liter. The produced water may also contain 20-40 mg/l of dissolved hydrocarbons including benzene, toluene, and xylene. This produced water is accompanied by immiscible hydrocarbons, typified by crude petroleum in amounts up to 0.1 w%; and it may also contain in suspension, insoluble solids, typically in amount up to say 0.1 w%.
Other aqueous media which may be treated by the process of this invention include various waste waters from industrial sources. For background on the problems generated by these liquids and some attempts to solve those problems, the following may be noted:
(i) European Pat. No. 251,691 to the Water Research Commission, Transvaal, South Africa as assignee of Buckley et al published Jan. 7, 1988; PA1 (ii) Simpson et al, The Effect of PH on the Nanofiltration of the Carbonate System in Solution, Desalination 64 (1987) pp 305-319. PA1 (iii) Bindoff et al, The Nanofiltration and Reuse of effluent from the Caustic Extraction Stage of Wood Pulping, Desalination 67 (1987) pp 455-465. PA1 (iv) Mickley, A Charged Ultrafiltration Membrane Process for Water Softening, IDA Journal 1 (1) (1985) March, pp 1-14 PA1 (v) Koros et al, Polymeric Membrane Materials for Solution Diffision Based Permeation Separations (private Communication). PA1 (i) Inorganic soluble salts typified by the normal soluble components of sea water; PA1 (ii) Inorganic insoluble salts typified by finely divided particles of e.g. calcium carbonate, calcium sulfate etc or by soluble salts present in excess of their solubility; PA1 (iii) Non-hydrocarbon organic matter typified by salts of lower aliphatic carboxylic acids such as acetic, propionic, butyric, etc. or naphthenic acids (these may be present as soluble or as non-soluble compositions) PA1 (iv) Hydrocarbons including soluble and insoluble hydrocarbons typified by the crude petroleum found in produced water.
No completely economically satisfactory solution to the problem has been found--particularly as it relates to the treatment of produced water on offshore drilling platforms--to yield a water of sufficient purity so that it meets governmental discharge limits applicable to water which is discharged into the sea.
Prior attempts to solve this problem have included the use of settling and/or skimming basins; but these have not proven to be economically desirable because inter alia they are characterized by size and weight which is undesirably high when measured against the limitations of e.g. an off-shore drilling platform.
It is an object of this invention to provide a novel process for treating an aqueous medium containing hydrocarbon liquid to attain a product aqueous medium containing a lesser amount of hydrocarbon. Other objects will be apparent to those skilled in the art.